This invention relates to memory devices, and more particularly to memory modules having on-board processors.
A conventional computer system 10 shown in FIG. 1 includes a central processing unit (xe2x80x9cCPUxe2x80x9d) 12, such as a microprocessor, that is coupled to a bus bridge 16, memory controller or the like. The CPU 12 is also typically coupled to a cache memory 18 to allow instructions and data to be more frequently accessed by the CPU 12. The bus bridge 16 allows the CPU 12 to receive program instructions from a system memory 20. The CPU 12 can also write data to and read data from the system memory 20 through the bus bridge 16. The CPU 12 also preferably transfers video data from the system memory 20 to a display system including a graphics processor or graphics accelerator 24, a video RAM 26, and a conventional display 28, such as a cathode ray tube (xe2x80x9cCRTxe2x80x9d), liquid crystal display (xe2x80x9cLCDxe2x80x9d) or field emission display (xe2x80x9cFEDxe2x80x9d). The graphics accelerator 24 processes graphics data to free up the CPU 12 from performing that function. The graphics accelerator 24 writes video data to and reads video data from the video RAM 26, and generates a video signal that is applied to the display 28. The bus bridge 16 also interfaces the CPU 12 to a peripheral bus 30, such as a peripheral component interconnect (xe2x80x9cPCIxe2x80x9d) bus. The peripheral bus 30 is, in turn, coupled to at least one mass storage device, such as a disk drive 32 and a CD ROM drive 34, and at least one user interface device, such as a keyboard 36 and a pointing device 38. The computer system 10 may, of course, contain a greater or lesser number of components.
As shown in FIG. 2, the system memory 20 is generally in the form of several integrated circuit memory devices 40, such as dynamic random access memories (xe2x80x9cDRAMsxe2x80x9d) and which may be Advanced Technology (xe2x80x9cATxe2x80x9d) Drams, such as RAMBUS DRAMs (xe2x80x9cRDRAMsxe2x80x9d) or synchronous link DRAMs (xe2x80x9cSLDRAMsxe2x80x9d), mounted on a printed circuit board 42. The resulting memory module 44 is then removably plugged into a mother-board 46 of a computer system 10 (FIG. 1). The size of the computer system""s memory can be increased by simply plugging additional memory modules 44 into the mother-board 46. Memory modules 44 are commercially available in standardized configurations, such as a single in-line memory module (xe2x80x9cSIMMxe2x80x9d) and a double in-line memory module (xe2x80x9cDIMMxe2x80x9d). The memory modules 44 are electrically coupled to a memory controller 50 or other device (not shown) mounted on the mother-board 46 using standardized memory interfaces. These standardized memory interfaces generally include a data bus, an address bus, and a control/status bus.
Transferring data and instructions to and from the system memory 20 is a frequent event, and it can consume a substantial percentage of the available processing time of the CPU 12. To reduce the processing burden on the CPU 12, direct memory access procedures may be employed in which data and instructions are transferred to and from the system memory 20 by device other than the CPU 12. For example, instructions may be transferred directly from a basic input-output system (xe2x80x9cBIOSxe2x80x9d) read only memory (xe2x80x9cROMxe2x80x9d) (not shown) or from a disk drive 32 (FIG. 1) for subsequent reading and execution by the CPU 12. Graphics data stored in the system memory 20 may be transferred directly to the graphics accelerator 24 without the use of the CPU 12. Direct memory accesses thus allow the CPU 12 to perform other functions during accesses to the system memory 20. Direct memory access may similarly be used to transfer data to and from the video RAM 26 without using the CPU 12.
Although direct memory access procedures can free-up the CPU 12 to perform other functions during a simple data transfer procedure, there are other memory intensive processing functions occurring in the computer system 10 that cannot be performed easily by devices other than the CPU 12. For example, xe2x80x9cdata miningxe2x80x9d is a procedure by which data stored in the system memory 20 is searched for the presence of predetermined patterns or values of characters. A data mining algorithm causes the CPU 12 to repetitively read data from the system memory 20 and compare the read data to the predetermined data. Since this procedure requires that data not only be transferred from the system memory 20 but also be compared to the predetermined data, the CPU 12 is normally required to perform this procedure. The processing power of the CPU 12 is also required to execute a wide variety of other memory intensive algorithms, such as speech recognition algorithms.
Attempts have been made to free CPUs from executing memory intensive algorithms by placing dedicated processors on memory modules, such as the memory module 44 shown in FIG. 2. An example of a conventional memory module containing on-board processing capability is shown in FIG. 3. The memory module 60 includes several memory devices 62, such as DRAMs, mounted on a printed circuit substrate 64. The module 60 also includes a respective dedicated processor 70 coupled to each memory device 62 though a bus system 72. A single program memory 74 receives and then stores instructions coupled from appropriate circuitry (not shown) on the mother-board 46FIG. 2) through a program bus 76. The program memory 74 supplies the stored instructions to all of the processors 70. Generally the same or related instructions are supplied to all of the processors 70 so that the processors 70 operate in parallel. The processor 70 is generally a reduced instruction set computer (xe2x80x9cRISCxe2x80x9d), although more conventional processors may also be used.
In operation, prior to performing a memory intensive function, the module 60 is programmed by supplying the program memory 74 through the program bus 76 with instructions to perform a predetermined algorithm. The processors 70 then fetch the instructions stored in the program memory 74, and perform the corresponding functions. These functions will normally include reading data from the memory devices 62 and writing data to the memory devices 62. Significantly, the CPU 12 of the computer system 10 need not be involved in performing these functions, although the CPU 12 may be involved in initially providing the instructions to the program memory 74. As a result, the CPU 12 is free to perform other functions during these memory intensive operations. The memory module 60, may, of course, be used as a conventional memory module, in which case it interfaces with the mother-board 46 through a conventional bus system 80 including a data bus, address bus, and control/status bus. The bus system 80, as well as the program bus 76, generally interface with the mother-board 46 through an edge connector 88a,b. 
The memory module 60 shown in FIG. 3 can be effective in greatly improving the processing power of computer systems 10 performing memory intensive algorithms. Its primary limitation is the requirement that the mother-board 46 be specially adapted to interface with the memory module 60. More specifically, the mother-board 46 must include a bus for interfacing with the program bus 76, as well as appropriate circuitry for supplying the instructions to the bus 76. Different memory modules 60 may, of course, use different processors 70, thereby requiring that the instruction set provided by the mother-board 46 be matched to the processor 70. Additionally, the edge connector 88 is inherently different from a conventional memory a module edge connector because it must include terminals for the processor bus 76. Computer systems 10, and hence mother-boards 46, are available from a wide variety of manufacturers, and so are memory modules. As a result, conventional memory modules 60 that include on-board processors 70 must be specially matched to specific computer systems 10, thus making the use of such memory modules 60 inconvenient and unduly expensive.
It would greatly facilitate the use of memory modules containing processors and make them more marketable if they could electrically and physically interface with conventional computer system mother-boards without any hardware modifications. However, the need to supply the modules with instructions adapted for specific processors makes standardization apparently impractical.
A method and apparatus for accessing and processing data in a system memory of a computer system. The system memory is mounted on a memory module that is coupled to the computer system through a data bus and an address bus. The memory module also contains a processor and a program memory. Instructions are transferred from the data bus to the program memory responsive to a first set of addresses on the address bus. The processor may then execute the stored instructions from the program memory. The system memory may also be accessed by the computer system through the data bus responsive to a second set of addresses on the address bus, at least some of which are different from the addresses in the first set. As a result, the memory module can interface with the computer system in the same manner as a conventional memory model not containing any on-board processing capability.